The present invention is directed to a method for sustaining the catalytic activity of a catalyst composition, and in particular to a method for sustaining the catalytic activity of a catalyst composition used in the production of aromatic carbonates.
A useful method for the production of aromatic carbonates includes the oxidative carbonylation of aromatic hydroxy compounds, with carbon monoxide and oxygen, which is typically catalyzed by a catalyst composition comprising a Group 8, 9 or 10 metal catalyst, various metal co-catalysts, a salt source, optionally an activating solvent, and optionally a base source. The oxidative carbonylation of aromatic hydroxy compounds is typically performed under elevated reactor pressures between about 5 MPa and about 15 MPa, due to the low solubility of both carbon monoxide and oxygen in typical aromatic hydroxy reagents such as phenol, and elevated reactor temperatures between about 50xc2x0 C. and about 120xc2x0 C. to accelerate reaction rates. On a commercial scale, the oxidative carbonylation of aromatic hydroxy compounds could be facilitated if reaction conditions, such as temperature and pressure, could be periodically varied during the course of the reaction, e.g., during temporary reactor shutdown periods, without reducing the activity of the catalyst composition. However, what is typically observed when the elevated pressure in a catalytic oxidative carbonylation reaction of an aromatic hydroxy compound is temporarily reduced to about atmospheric pressure, specifically at reaction mixture temperatures above about 60xc2x0 C. is an irreversible decrease in the activity of the catalyst composition once the original reaction conditions are re-established. Consequently, a long felt yet unsatisfied need exists for new and improved methods for sustaining the activity of catalyst compositions during and after changes in the reaction conditions of a catalytic oxidative carbonylation reaction.
In one embodiment, the present invention is directed to a method for sustaining the catalytic activity of a carbonylation catalyst composition, after changes in reaction conditions, in a catalytic oxidative carbonylation reaction contained in a reactor vessel in which a reaction mixture comprising said carbonylation catalyst composition is disposed, said method comprising the following steps:interrupting said carbonylation reaction with a first reaction condition changing step, which comprises first lowering the temperature of the reaction. mixture from a first temperature T1, to a second temperature T2, followed by lowering the pressure in said reactor vessel from a first pressure P1, to a second pressure P2; optionally, a resting step, which comprises maintaining said reaction mixture at said second temperature T2, and maintaining the pressure in said reactor vessel at said second pressure P2, for a predetermined amount of time; andre-establishing said carbonylation reaction with a second reaction condition changing step, which comprises first raising the pressure in said reactor vessel from said second pressure P2 to a third pressure P3, followed by raising the temperature of said reaction mixture from said second temperature T2 to a third temperature T3; wherein the level of catalytic activity of said carbonylation catalyst composition under said third temperature T3, and said third pressure P3, is comparable to a level of catalytic activity which would be present in an equivalent catalytic oxidative carbonylation reaction in which the temperature and pressure were changed from said first temperature T1 and said first pressure P1 directly to said third temperature T3 and said third pressure P3, in the absence of said first reaction condition changing step, and said optional resting step.
The method of the present invention is suitable for a typical carbonylation catalyst compositions comprising a Group 8, 9, or 10 catalyst source, which can catalyze the production of aromatic carbonates via the oxidative carbonylation of aromatic hydroxy compounds with oxygen and carbon monoxide.
In one embodiment, the present invention is directed to a method for sustaining the catalytic activity of a carbonylation catalyst composition, after changes in reaction conditions in a catalytic oxidative carbonylation reaction. In the context of the present invention, the phrase xe2x80x9csustaining the catalytic activityxe2x80x9d is defined as prolonging the amount of time during which the catalyst composition is active at producing the desired aromatic carbonate at a predetermined reaction rate. The xe2x80x9cpredetermined reaction ratexe2x80x9d is a rate which is comparable, e.g., having a value that is between about 80% and about 120% of the reference value, to a reaction rate that would be present in a similar oxidative carbonylation reaction in the absence of any changes to the reaction conditions. Herein, the reaction rate is defined in terms of the weight percent of desired aromatic carbonate produced during a predetermined amount of reaction time, e.g., weight % of desired carbonate=[(moles of desired carbonate)(molecular weight of desired carbonate)/mass of reaction mixture].
In the context of the present invention, the term xe2x80x9creaction conditionsxe2x80x9d is meant to include, but is not limited to, reactor vessel pressure, reactor vessel temperature, reaction mixture temperature, agitation rate, gas flow rates (e.g., carbon monoxide flow rate and oxygen flow rate), gas mixture composition (e.g., ratio of carbon monoxide to oxygen), the weight % of various components of the reaction mixture including, but not limited to, weight % of aromatic hydroxy compound, weight % of desired carbonate and weight % of water, and the pH of the reaction mixture.
In the present invention, the term xe2x80x9creaction mixturexe2x80x9d is defined as the total mixture of compounds and gases which results from the carbonylation of an aromatic hydroxy compound using oxygen, carbon monoxide, and a carbonylation catalyst composition typically comprising a Group 8, 9 or 10 metal source as a catalyst, and optionally at least one member selected from the group consisting of a first inorganic co-catalyst (IOCC), a second IOCC, a salt source, an activating solvent, a base source, and any mixtures thereof. During the carbonylation reaction, the reaction mixture typically further comprises the desired aromatic carbonate, unreacted aromatic hydroxy compound, and byproducts of the carbonylation reaction which include, but are not limited to, water, aryl ethers, poly-aromatic hydroxy compounds, phenyl salicylate, and aromatic carbonates other than the desired aromatic carbonate. Suitable types of aromatic hydroxy compounds include, but are not limited to, monocyclic aromatic compounds comprising at least one hydroxy group, and polycyclic aromatic compounds comprising at least one hydroxy group. Illustrative examples of suitable aromatic hydroxy compounds include, but are not limited to, phenol, alkylphenols, alkoxyphenols, bisphenols, biphenols, and salicylic acid derivates (e.g., methyl salicylate).
The carbonylation catalyst composition present in the reaction mixture typically comprises a first metal source selected from a Group 8, 9 or 10 metal source. Typical Group 8, 9 or 10 metal sources include ruthenium sources, rhodium sources, palladium sources, osmium sources, iridium sources, platinum sources, and mixtures thereof. In one embodiment, about 1 ppm to about 10000 ppm of a Group 8, 9, or 10 metal source is present in the catalyst composition. In another embodiment, about 1 ppm to about 1000 ppm of a the Group 8, 9, or 10 metal source is present in the catalyst composition. In yet another embodiment of the present invention, about 1 ppm to about 100 ppm of a Group 8, 9, or 10 metal source is present in the catalyst composition. A typical Group 8, 9, or 10 metal source is a palladium source, including palladium compounds. As used herein, with respect to metal sources in general, the term xe2x80x9ccompoundxe2x80x9d includes inorganic , coordination and organometallic complex compounds. The compounds are typically neutral, cationic, or anionic, depending on the charges carried by the central metal and the coordinated ligands. Other common names for these compounds include complex ions (if electrically charged), Werner complexes, and coordination complexes. The Group 8, 9, or 10 metal source is typically present in the reaction mixture in a homogeneous form that is substantially soluble in the reaction mixture, or alternatively in a heterogeneous form which is substantially insoluble in the reaction mixture, including metal sources supported on substrates and polymer bound metal sources. Examples of suitable palladium sources include, but are not limited to, palladium sponge, palladium black, palladium deposited on carbon, palladium deposited on alumina, palladium deposited on silica, palladium halides, palladium nitrates, palladium carboxylates, palladium acetates, palladium salts of xcex2-diketones, palladium salts of xcex2-ketoesters, and palladium compounds containing at least one of the following ligands: carbon monoxide, amine, nitrite, nitrile, isonitrile, phosphine, phosphite, phosphate, alkoxide, alkyl, aryl, silyl or olefin.
As used herein, the term xe2x80x9cinorganic co-catalystxe2x80x9d(IOCC) includes any catalyst component that contains a metal element, which is present in the catalyst composition in addition to the first metal source. Typically, one or two IOCC""s are present in the catalyst composition, and thus are present in the reaction mixture as a second metal source and a third metal source, respectively. Typical IOCC""s include, but are not limited to, compounds selected from the group consisting of Group 4 metal sources, Group 7 metal sources, Group 8 metal sources, Group 9 metal sources, Group 11 metal sources, Group 12 metal sources, Group 14 metal sources, Group 15 metal sources, Lanthanide sources, and mixtures thereof. Examples of IOCC sources include, but are not limited to, titanium sources, manganese sources, iron sources, cobalt sources, copper sources, zinc sources, lead sources, bismuth sources, and cerium sources. Suitable forms of IOCC sources include, but are not limited to, elemental metals, metal oxides, and metal compounds in stable oxidation states. For example, in one embodiment a first IOCC is initially present in the carbonylation catalyst composition as lead (II) oxide. Other suitable lead sources include, but are not limited to, lead halide compounds (e.g., lead (II) bromide), lead alkoxy compounds (e.g., lead (II) methoxide), lead aryloxy compounds (e.g., lead (II) phenoxide), organometallic lead compounds having at least one lead-carbon bond, (e.g., alkyl lead compounds such as tetraethyllead (IV)), and lead compounds containing at least one of the following ligands: carbon monoxide, amine, nitrite, nitrile, isonitrile, cyanide, phosphine, phosphite, phosphate, alkoxide, alkyl, aryl, silyl or olefin. Mixtures of lead sources are also suitable. The IOCC compounds are typically neutral, cationic, or anionic, depending on the charges carried by the central atom and the coordinated ligands. The IOCC compounds are typically present in the reaction mixture in a homogeneous form that is substantially soluble in the reaction mixture, or alternatively in a heterogeneous form which is substantially insoluble in the reaction mixture, including metal sources supported on substrates and polymer bound metal sources. In one embodiment, about 1 equivalent to about 1000 equivalents of at least one IOCC source, versus the amount of a Group 8, 9, or I0 metal source, is present in the reaction mixture. In another embodiment, about 1 equivalent to about 500 equivalents of at least one IOCC source, versus the amount of a Group 8, 9, or 10 metal source, is present in the reaction mixture. In yet another embodiment of the present invention, about 1 equivalent to about 100 equivalents of at least one IOCC source, versus the amount of a Group 8, 9, or 10 metal source, is present in the reaction mixture. For example, in one embodiment, about 1500 parts per million (ppm) of lead (II) oxide, versus about 27 ppm of palladium 2,4-pentanedionate, are present in the carbonylation catalyst composition in the reaction mixture.
Typically, the carbonylation catalyst composition in the reaction mixture further comprises at least one salt source. Illustrative examples of salt sources present in the carbonylation catalyst composition include, but are not limited to, carboxylates, acetates, benzoates, nitrates, phosphates, phosphites, tetraarylborate, sulfates, alkylsulfonates, arylsulfonates, alkali halides, alkaline-earth halides, guanidinium halides, and onium halides (e.g., ammonium halides, phosphonium halides, and sulfonium halides). Typical onium cations contain organic residues, which include C1-C20 alkyl, C6-C10 aryl, or alkyl-aryl combinations thereof. In one embodiment, about 1 equivalent to about 100000 equivalents of a salt source, versus the amount of a Group 8, 9, or 10 metal source, is present in the reaction mixture. In another embodiment, about 1 equivalent to about 10000 equivalents of a salt source, versus the amount of a Group 8, 9, or 10 metal source, is present in the reaction mixture. In yet another embodiment of the present invention, about 1 equivalent to about 1000 equivalents of a salt source, versus the amount of a Group 8, 9, or 10 metal source, is present in the reaction mixture. For example, in one embodiment, about 17000 ppm of tetraethylammonium bromide (TEAB), versus about 27 ppm of palladium 2,4-pentanedionate, are present in the carbonylation catalyst composition in the reaction mixture.
In one embodiment, the catalyst composition further comprises at least one activating solvent. Typically, about 1% to about 60% by volume of activating solvent, based on the total volume of the reaction mixture, is used. In another embodiment of the present invention, about 1% to about 40% by volume of activating solvent, based on the total volume of the reaction mixture is used. In yet another embodiment of the present invention, about 1% to about 10% by volume of activating solvent based on the total volume of the reaction mixture is used. Suitable activating solvents include, but are not limited to, polyethers (e.g. compounds containing two or more Cxe2x80x94Oxe2x80x94C linkages), carboxylic acid amides, sulfones, and nitriles. Polyethers are typically aliphatic or mixed aliphatic-aromatic polyethers. Suitable aliphatic polyethers include, but are not limited to, diethylene glycol dialkyl ethers such as diethylene glycol dimethyl ether (hereinafter xe2x80x9cdiglymexe2x80x9d), triethylene glycol dialkyl ethers such as triethylene glycol dimethyl ether (hereinafter xe2x80x9ctriglymexe2x80x9d), tetraethylene glycol dialkyl ethers such as tetraethylene glycol dimethyl ether (hereinafter xe2x80x9ctetraglymexe2x80x9d), polyethylene glycol dialkyl ethers such as polyethylene glycol dimethyl ether and crown ethers such as 12-crown-4 (1,4,7,10-tetraoxacyclododecane), 15-crown-5 (1,4,7,10,13-pentaoxacyclopentadecane) and 18-crown-6 (1,4,7,10,13,16-hexaoxacyclooctadecane). Illustrative examples of mixed aliphatic-aromatic polyethers include, but are not limited to, diethylene glycol diphenyl ether and benzo-18-crown-6. Mixtures of polyethers are also suitable. Another example of a suitable activating solvent is a carboxylic acid amide. Typically, fully substituted aliphatic, fully substituted aromatic, or fully substituted heterocyclic amides (containing no NH groups including the amide nitrogen) are used. Illustrative examples of carboxylic acid amides include, but are not limited to, dimethylformamide, dimethylacetamide, dimethylbenzamide and N-methylpyrrolidinone. A further example of a suitable activating solvent is a sulfone. Suitable types of sulfones for the present invention include, but are not limited to, aliphatic sulfones, aromatic sulfones, and heterocyclic sulfones. Illustrative examples of suitable sulfones include, but are not limited to, dimethyl sulfone, diethyl sulfone, diphenyl sulfone, and sulfolane (e.g., tetrahydrothiophene-1,1-dioxide). In yet another embodiment of the present invention, a suitable activating solvent is a nitrile solvent. Suitable nitrile solvents include, but are not limited to, C2-C8 aliphatic or C7-C10 aromatic mononitriles or dinitriles. Illustrative mononitriles include, but are not limited to, acetonitrile, propionitrile, and benzonitrile. Illustrative dinitriles include, but are not limited to, succinonitrile, adiponitrile, and benzodinitrile. For example, in one embodiment the catalyst composition comprises acetonitrile, which is present at about 33 volume % based on the total volume of the reaction mixture.
In one embodiment of the present invention, the carbonylation catalyst composition further comprises at least one base source. Suitable types of base sources include, but are not limited to, basic oxides, hydroxides, mono-alkoxides, poly-alkoxides, monocyclic aryloxides, polycyclic aryloxides, and tertiary amines. Illustrative examples of suitable base sources include, but are not limited to, sodium hydroxide, lithium hydroxide, potassium hydroxide, tetraalkylammonium hydroxides (e.g. tetramethylammonium hydroxide, tetraethylammonium hydroxide, methyltributylammonium hydroxide, and tetrabutylammonium hydroxide) sodium phenoxide, lithium phenoxide, potassium phenoxide, tetraalkylammonium phenoxides (e.g. tetramethylammonium phenoxide, tetraethylammonium phenoxide, methyltributylammonium phenoxide, and tetrabutylammonium phenoxide), and triethyl amine. In one embodiment, about 1 equivalent to about 10000 equivalents of a base source, versus the amount of a Group 8, 9, or 10 metal source, is present in the reaction mixture. In another embodiment, about 1 equivalent to about 1000 equivalents of a base source, versus the amount of a Group 8, 9, or 10 metal source, is present in the reaction mixture. In yet another embodiment of the present invention, about 1 equivalent to about 500 equivalents of a base source, versus the amount of a Group 8, 9, or 10 metal source, is present in the reaction mixture.
An element in the present invention is the order in which changes to the reactions conditions are carried out. For example, in a typical oxidative carbonylation reaction where the reaction mixture has a temperature between about 80xc2x0 C. and 120xc2x0 C., and the reactor vessel is pressurized to between about 6 MPa and 9 MPa with carbon monoxide and oxygen, it is critical to the activity of the carbonylation catalyst composition that a decrease in the elevated reactor vessel pressure, especially if the decrease in pressure is to about atmospheric pressure, be preceded by a reduction in reaction mixture temperature to about 60xc2x0 C. or lower. Failure to perform these changes in reaction conditions in this order, results in an irreversible reduction in activity of the catalyst composition, under the oxidative carbonylation conditions described above. Similarly, when re-establishing the original reaction conditions it is critical that the reactor vessel pressure be increased before the reaction mixture temperature is increased in order to retain a level of activity in the catalyst composition which is comparable to the level of activity which was present prior to any changes in reactor vessel pressure and reaction mixture temperature. In one embodiment, the final reactor vessel pressure and final reaction mixture temperature upon re-establishment of the carbonylation reaction, are about equivalent to the initial reactor vessel pressure and initial reaction mixture temperature.